In recent years, due to increasingly serious traffic congestion in cities, subway projects are developed in more and more cities. Tunnel boring machines have a dominant position in construction of subway projects in cities and make up indispensable common techniques in construction of tunnels, owing to that the tunnel boring machines have small effects on environments and a wide range of application, and are suitable for constructions with large depth, high earth pressure and high water pressure, and low in costs.
Over the past thirty years, shield tunneling technologies developed at full speed with varied types of shields. Currently, the tunnel boring machines have circular, rectangular, multi-circle-spliced, horseshoe-like and the like sections. The circular sections are the most commonly used sections owing to a lot of advantages. However, tunnels with the circular sections have defects of low utility rate of internal space. The rectangular sections are also employed in constructions, tunnels with the rectangular sections are high in utility rate of internal space but also have obvious defects such as large pressures on segments, complex designs and splicing, high costs and the like. Multi-circle-spliced tunnels are high in utility rate of space, but there are large difficulties in constructions, designs of segments and designs of excavating mechanisms and drive devices of tunnel boring machines, resulting in large manufacturing costs of complete machines. Excavated sections of horseshoe-like tunnel boring machines are nonstandard horseshoe-shaped sections, and horseshoe-like tunnel boring machines include a plurality of cutterheads and drive mechanisms. The horseshoe-like tunnel boring machines are complex in structure with high costs of designs and maintenances, and costs of segment erection and latter constructions are high, therefore, the horseshoe-like tunnel boring machines are not suitable for large-scale promotion and use.